1. Field of the Invention
The present invention relates to a liquid crystal apparatus having an external drive circuit connected thereto.
2. Related Background Art
Conventionally, a liquid crystal panel and an external drive circuit are mechanically and electrically connected together by a widely known method whereby a connection electrode of a film carrier tape on which a drive IC for example is mounted, is positioned facing an indium tin oxide (ITO) electrode of a liquid crystal panel, and both of the electrodes are mechanically and electrically connected together by thermocompression bonding using an isotropic conductive adhesive agent made of resin particles coated with metal particles or metal plated.
Another method is also known whereby a metal bump is formed on a connection electrode of a drive IC, and conductive paste or metal particles are interposed between the metal bump and the ITO electrode of a liquid crystal panel to mechanically and electrically connect together the metal bump and the ITO thin film.
According to the conventional technique, the wiring resistance from the external drive circuit to the liquid crystal material mainly depends on the wiring resistance of the ITO electrode itself.
A drive signal supplied to the liquid crystal material is subject to a delay .tau.=RC where R is a wiring resistance from the external drive circuit to the liquid crystal material, and C is an electrostatic capacitance between the upper and lower electrodes. This delay leads to a small drive margin. A liquid crystal, particularly a ferroelectric liquid crystal, which requires a small cell gap such as about 2 microns, inevitably makes the electrostatic capacitance C very large. It therefore becomes necessary to reduce the wiring resistance as small as possible.
In view of the above circumstances, according to a conventional technique, a method has been used whereby a narrow stripe metal film made of molybdenum, aluminum or the like is provided on the ITO thin film of a transparent stripe conductive film wired within a liquid crystal.
Such a metal film on the ITO thin film is provided also at the area outside of the liquid crystal cell because even such a small area has a large wiring resistance. If a fine wire made of molybdenum film or aluminum film is used, electrolysis action may occur under the condition of, e.g., a presence of water contents so that the fine molybdenum or aluminum film is subject to corrosion and broken out. From this reason, the whole area of the ITS electrode outside of the liquid crystal cell is covered with the metal film.
The metal film is likely to have surface oxidation. Therefore, the surface is covered with a thin metal oxide film having a thickness of, e.g., about 1000 to 3000 angstroms. This metal oxide film is generally an insulating material. Therefore, in order to ensure electrical connection between the connection electrode of a film carrier tape and the metal film facing the connection electrode, hard metal particles (e.g., nickel) have been used which can break the oxide metal film. Use of nickel particles causes point contacts between the particles and the connection electrode, resulting in variations of wiring resistance. Furthermore, nickel particles may sometimes break the metal film together with the metal oxide film, lowering the reliability of electrical connection.